An example robot may have a plurality of members forming the robot's legs and arms. The motion of these members may be controlled by actuators such as hydraulic cylinders and motors. The design of these actuators determines the performance characteristics of the robot such as how fast the robot can respond to commands and external disturbances. Design factors that affect performance of the robot may include rotary inertia of the actuator and gear ratio of a transmission coupled thereto, among other factors.